Add an explicit unit test for the workers exec and delay functions

I've wrote this test when checking the worker code for
https://progress.opensuse.org/issues/96710.

t/24-worker-overall.t

@@ -116,6 +116,30 @@ combined_like { $worker->log_setup_info }
 qr/.*http:\/\/localhost:9527,https:\/\/remotehost.*qemu_i386,qemu_x86_64.*Errors occurred.*foo.*bar.*/s,
   'setup info with parse errors';
 
+subtest 'delay and exec' => sub {
+    my $worker_mock = Test::MockModule->new('OpenQA::Worker');
+    $worker_mock->redefine(init => 42);
+
+    my %executed_code_paths;
+    my %expected_code_paths = map { $_ => 1 } qw(before_delay after_delay another_event);
+    Mojo::IOLoop->next_tick(
+        sub {
+            $executed_code_paths{before_delay} = 1;
+            note 'before delay';
+            Mojo::IOLoop->timer(
+                0 => sub {
+                    $executed_code_paths{another_event} = 1;
+                    note 'another event';
+                });
+            $worker->delay(0);
+            $executed_code_paths{after_delay} = 1;
+            note 'after delay';
+        });
+    is $worker->exec, 42, 'return code passed from init';
+    is_deeply \%executed_code_paths, \%expected_code_paths, 'all code paths executed'
+      or diag explain \%executed_code_paths;
+};
+
 subtest 'capabilities' => sub {
     my $capabilities = $worker->capabilities;